Delayed::Cron::Job

Delayed::Cron::Job is an extension to Delayed::Job that allows you to set cron expressions for your jobs to run repeatedly.

Installation

Add the following line to your application's Gemfile. Add it after the lines for all other delayed_job* gems so the gem can properly integrate with the Delayed::Job code.

gem 'delayed_cron_job'

And then execute:

$ bundle

If you are using delayed_job_active_record, generate a migration (after the original delayed job migration) to add the cron column to the delayed_jobs table:

$ rails generate delayed_job:cron
$ rake db:migrate

There are no additional steps for delayed_job_mongoid.

Usage

When enqueuing a job, simply pass the cron option, e.g.:

Delayed::Job.enqueue(MyRepeatedJob.new, cron: '15 */6 * * 1-5')

Or, when using ActiveJob:

MyJob.set(cron: '*/5 * * * *').perform_later

Any crontab compatible cron expressions are supported (see man 5 crontab). Cron parsing is handled by Fugit.

Scheduling

Usually, you want to schedule all existing cron jobs when deploying the application. Using a common super class makes this simple.

Custom CronJob superclass

app/jobs/cron_job.rb:

# Default configuration in `app/jobs/application_job.rb`, or subclass
# ActiveJob::Base .
class CronJob < ApplicationJob

  class_attribute :cron_expression

  class << self

    def schedule
      set(cron: cron_expression).perform_later unless scheduled?
    end

    def remove
      delayed_job.destroy if scheduled?
    end

    def scheduled?
      delayed_job.present?
    end

    def delayed_job
      Delayed::Job
        .where('handler LIKE ?', "%job_class: #{name}%")
        .first
    end

  end
end

Example Job inheriting from CronJob

Then, an example job that triggers E-Mail-sending with default cron time at noon every day:

app/jobs/noon_job.rb:

# Note that it inherits from `CronJob`
class NoonJob < CronJob
  # set the (default) cron expression
  self.cron_expression = '0 12 * * *'

  # will enqueue the mailing delivery job
  def perform
    UserMailer.daily_notice(User.first).deliver_later
  end
end

Automatic Scheduling after db:migrate

Jobs with a cron definition are rescheduled automatically only when a job instance finished its work. So there needs to be an initial scheduling of all cron jobs. If you do not want to do this manually (e.g. using rails console) or with your application logic, you can e.g. hook into the rails db:* rake tasks:

lib/tasks/jobs.rake:

namespace :db do
  desc 'Schedule all cron jobs'
  task :schedule_jobs => :environment do
    # Need to load all jobs definitions in order to find subclasses
    glob = Rails.root.join('app', 'jobs', '**', '*_job.rb')
    Dir.glob(glob).each { |file| require file }
    CronJob.subclasses.each(&:schedule)
  end
end

# invoke schedule_jobs automatically after every migration and schema load.
%w(db:migrate db:schema:load).each do |task|
  Rake::Task[task].enhance do
    Rake::Task['db:schedule_jobs'].invoke
  end
end

Now, if you run rails db:migrate, rails db:schema:load or rails db:schedule_jobs all jobs inheriting from CronJob are scheduled.

If you are not using ActiveJob, the same approach may be used with minor adjustments.

Changing the schedule

Note that if you have a CronJob scheduled and change its cron_expression in its source file, you will have to remove any scheduled instances of the Job and reschedule it (e.g. with the snippet above: rails db:migrate). This is because the cron_expression is already persisted in the database (as cron).

Details

The initial run_at value is computed during the #enqueue method call. If you create Delayed::Job database entries directly, make sure to set run_at accordingly.

You may use the id of the Delayed::Job as returned by the #enqueue method to reference and/or remove the scheduled job in the future.

The subsequent run of a job is only scheduled after the current run has terminated. If a single run takes longer than the given execution interval, some runs may be skipped. E.g., if a run takes five minutes, but the job is scheduled to be executed every second minute, it will actually only execute every sixth minute: With a cron of */2 * * * *, if the current run starts at :00 and finishes at :05, then the next scheduled execution time is at :06, and so on.

If you do not want longer running jobs to skip executions, simply create a lightweight master job that enqueues the actual workload as separate jobs. Of course you have to make sure to start enough workers to handle all these jobs.

Contributing

1. Fork it ( https://github.com/codez/delayed_cron_job/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

License

Delayed::Cron::Job is released under the terms of the MIT License. Copyright 2014-2023 Pascal Zumkehr. See LICENSE for further information.